Sources of Weather Information in X-Plane 12

There are several places in X-Plane where information about weather are available. This tech note describes each of them and how they relate to each other. Different sources are highly likely to return different information, by design. Weather conditions at any given point will be different to the weather at any other point, in both location and time.

The Weather Configuration

While this is not really a source of weather information, it does have an impact on the weather. When set to 'static weather' mode, very specific conditions may be set. These conditions are applied when you start your flight as a starting point. The simulator's weather system will then, from this starting point, add more details specifically including a small amount of randomness which changes across both time and distance from your starting airport. Any weather information found from any of the simulator's other systems should be expected to be similar to, but not an exact match for, static weather.

The Map Window

It is possible to use the map to get basic weather information about an airport, by clicking on the airport's icon to show the 'Airport Details' popout. On the 'Details' tab, an item labelled "Conditions", or "Current Conditions" in 12.1.0b5 and higher, shows the weather at the clicked airport at the exact time the popout was opened. The displayed information does not change after the popout has opened, so will become stale. Although the text given is similar to an ATIS message, it is not ATIS; it has no rounding, corrections or unit adjustment applied.

ATIS Transmissions

Many airports will offer an ATIS radio service. This is accessed using your aircraft's radio. The conditions given are those that were present at the time and location of recording of the ATIS message, and that recording will have a validity of either 30 or 60 minutes. Therefore, you should expect ATIS messages to differ from current conditions to some extent especially towards the end of their validity period. If conditions change significantly, a 'special ATIS' message will be issued and the ATIS identifier will be changed. ATIS frequencies are listed in the ATC dialog and on the map.

AWOS Transmissions

Similar to ATIS, AWOS messages differ in that they are fully automated messages based on conditions at the time and location of transmission. They are differentiated from ATIS messages by the absence of an ATIS identifier, and the prefix "AUTOMATED WEATHER OBSERVATION".

The simulator provides AWOS services for untowered airports and ATIS for towered airports, where the airport is defined as having an automated weather service. Both ATIS and AWOS services have rounding applied to wind direction and will use local temperature- and elevation-corrected pressure units, and regional units and phrasing.

"Request Departure Information" ATC call

At airports with a tower but no ATIS service, you can request departure information from ATC before you request taxi. This provides the weather conditions at the exact time of the radio response, at the airport's reference point.

"Request Weather" ATC call

While you are in contact with any controller that is based at a specific airport, including regional controllers, you may request current weather at their location. This provides the weather conditions at the exact time of the radio response, at the airport's reference point.

"Request Weather At…" ATC call

While you are flying a planned (IFR) route under ATC control, or if you are receiving flight following and have programmed named waypoints into your FMS, you may request weather conditions along your route from most ATC controllers. This provides the weather conditions at the location of the navaid, at the exact time of the radio response.

Pressure in some ATC messages

Many ATC responses from controllers will include QNH settings. For airport-type controllers (clearance, ground and tower), this pressure will be valid at the time of the call at the exact location of the airport. For regional or tracon/approach controllers, the pressure given will be the single pressure value used for the controller's entire airspace. Currently airspace segments are not simulated. A regional controller, especially a large one, is likely to give you a different QNH value to the one given by an airport.

"/sim/weather/aircraft/" Datarefs

These provide an instantaneous readout of the exact conditions at your aircraft's location.

"/sim/weather/region/" Datarefs

These provide an instantaneous readout of the base conditions for the region surrounding your aircraft; at the time of writing this is approximately one square degree. These conditions will not match conditions at any specific point within that region, since the weather at any given point is also based upon local information where possible (i.e. METAR data), and is further affected by the weather simulation's inherent random variation.

METAR files

These are snapshots of the current weather at an airport at a particular time in the past, used as a data source by X-Plane's 'Real Weather' mode. While many are updated hourly or more, others may not be updated for significant periods of time. They are inherently data reflecting a time in the past.

To produce X-Plane's weather in 'Real Weather' mode, these are blended with another datasource which is based on a forecast of regional weather in the near future. This blending of point samples from the past with a generalised regional forecast for the future, plus the small amount of randomness layered onto the results, means that the simulator's weather should be similar to actual conditions but will rarely if ever be an exact match with any other source of weather information.

External Websites

External sources should never be used for obtaining weather conditions in the simulator, even when flying in 'Real Weather' mode. They are highly unlikely to match due to the random elements to X-Plane's weather simulation, different data sources, and differences in the way that the various data-sources are processed.

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